Skin tissue, as the natural protective layer of the outermost layer of the human body, often faces serious injury due to various internal and external factors. Common causes of skin injury include the factors such as exogenous wounds, endogenous or exogenous inflammation, immune responses and the like. In addition to accidents that cause skin injury, the treatments of many diseases often result in different skin injuries or scar depositions after the injuries due to the healing process.
The purpose of radiation therapy is to minimize the injuries to normal cells while destroying tumor cells. Considering the harmful side effects of radioactive rays in treating tumor cells, the strength of the side effect depends on the dose of radiation and the sensitivity of the irradiated skin tissue to radioactive rays. When the radioactive rays (whether it is ionizing radiation, such as X-rays or gamma rays, or particle radiation, such as neutron beams or alpha-particle beams) generated during the radiotherapy penetrate the body tissues, the atoms after being bombarded lose their outer electrons, thus generating a large amount of active free radicals inside the cells. These free radicals can interact with biological macromolecules such as DNA, proteins, membrane lipids, etc., disrupting their function and ultimately leading to cell dysfunction or death. The most common side effect of radiotherapy in clinical pathology is the radiation skin injury. In many tumor subtypes with effective radiotherapy (such as head and neck cancer, nasopharyngeal cancer, chest and abdomen tumors, etc.), it is often accompanied by very serious skin injuries. Therefore, radiotherapy protectants are often applied in the clinic before and after radiotherapy to achieve the effect of protecting skin tissue.
The ideal radiotherapy protectants should meet the following requirements:    1) must show significant radiotherapy protection effect;    2) must exhibit a certain degree of radiotherapy protection effect on most organs;    3) must be able to be administered by a good patient compliance route;    4) must have acceptable toxicity and protective time-window effect;    5) both the active ingredient(s) and the preparation complex composition thereof must have good stability;    6) can be widely compatible with other drugs.
For the route of administration, the most acceptable routes of administration should be oral administration, skin administration and intramuscular injection. Moreover, the skin administration can significantly reduce side effects such as hypotension, nausea, etc. as compared with intramuscular injection or oral administration, because the time required for the drug to be absorbed into the circulatory system through the skin is longer than that of the intravenous injection, the time reaching the peak of the blood concentration is also delayed. More importantly, the skin administration has a good compliance for the patient, and the operation is simple, time-saving and labor-saving for the medical staff.
Although the demand for skin tissue protection and reparation preparations used to treat corresponding radioactive inflammation or skin injury caused by radiotherapy is great in clinic, currently, there are no corresponding mature and reliable products available.